The present invention relates to a high purity neodymium-based rare earth permanent magnet of which magnetic properties are remarkably improved in comparison to conventional neodymium-based rare earth permanent magnets by highly purifying the magnet materials, and to a method for producing such a neodymium-based rare earth permanent magnet.
In recent years, permanent magnets are being applied to various fields pursuant to significant advances, and improvement of their performance and development of new devices are being conducted day by day. In particular, the widespread use of permanent magnets in the fields of IT, automobiles, household appliances and FA is remarkably increasing from the perspective of energy conservation and environmental countermeasures.
Permanent magnets are used, for example, in voice coil motors of hard disk drives and optical pickups of DVD/CD drives in relation to personal computers, in micro speakers and vibration motors in relation to portable phones, and in various motors such as servo motors and linear motors in relation to household appliances and industrial devices. Moreover, over 100 permanent magnets are used in a single electric vehicle such as an HEV.
As permanent magnets, known are Alnico magnets, Ferrite magnets, samarium-cobalt (SmCo) magnets, neodymium (NdFeB) magnets and the like. In recent years, the R&D of neodymium magnets is particularly active, and various efforts are being exerted for achieving higher performance of such neodymium magnets. A neodymium magnet is normally configured from a ferromagnetic Nd2Fe14B4 intermetallic compound (main phase), a paramagnetic B-rich phase, a nonmagnetic Nd-rich phase, and oxides and the like as impurities. In addition, efforts for improving the magnetic properties are being exerted by adding various types of elements thereto.
For example, Patent Document 1 discloses that the magnetic properties are significantly improved by simultaneously adding Co, Al, Cu and Ti to an R—Fe—B-based rare earth permanent magnet (wherein R is one or more types among Nd, Pr, Dy, Tb, and Ho), and Patent Document 2 discloses that the maximum energy product (BH)max can become 42 MGOe or more by adding Ga while adjusting the composition.
Other methods are also known for improving the magnetic properties; namely, the method of introducing a moderate amount of oxygen, which is an impurity that causes the magnetic properties to deteriorate (Patent Document 3), the method of increasing the coercive force by suppressing the growth of the main phase crystal grains as a result of the fluorine, which was added in a moderate amount, being unevenly distributed at the grain boundary of the magnet (Patent Document 4), and the method of improving the performance of the magnet by reducing the B-rich phase and the R-rich phase that cause the magnetic properties to deteriorate, and increasing the R2Fe14B phase as a main phase (Patent Document 5).
As described above, various attempts are being made in order to improve the magnetic properties such as by adding new types of component elements (rare earth elements, transition metal elements, impurity elements and the like), by adjusting the composition of the R—Fe—B-based rare earth permanent magnet, and otherwise by adjusting the crystal orientation. However, since all of these methods complicate the production process, it cannot be said that these methods are suitable for stable mass production.    Patent Document 1: JP 2000-331810 A    Patent Document 2: JP H06-231921 A    Patent Document 3: JP 2005-051002 A    Patent Document 4: International Publication No. WO2005/123974    Patent Document 5: JP H07-045413 A